The target_dir is created by Kiwi. Kiwi implements the complete logic for this like e.g. if it already exists kiwi will also fail.
Checking whether the parent dir is writable at the place it was done before this fix, has no impact. It will fail 0,0001 sec faster, which IMHO is irrelevant.
However we are actively looking for that error now and display an log.error msg accordingly without involving concrete Info that this error is coming from kiwi.
After the last merged PRs berrymill is broken...